FIG. 7 shows an external view structure of a conventional food fryer, and FIG. 8 shows a sectional view of an oil layer area and a water layer area in the conventional food fryer:                1 is the oil layer area for storing food frying oil; 2 is the water layer area; 3 is a heat source such as a heating burner; 4 is an air cooling tube formed by a means such as welding on the outer wall of the oil layer area 1; 10 is bits of fried batter; 11 is a water discharge cock; 12 is a net; 14 is an oil discharge cock; 15 is an adjusting wheel or a roller for adjusting a balance of the food fryer on a floor surface; 16 is an air outlet; 17 is a thermostat for controlling the heat source 3.        
Now, oil and water in the food fryer are respectively separated into the oil layer area 1 and the water layer area 2 due to the difference in specific gravity thereof, where the oil is heated by the heat source 3 to fry meat, fish, vegetables, etc.
The cooling means such as the air cooling tube 4 provided below the heat source 3 insulates thermal conduction caused through the heated oil at a high temperature and by bits of fried batter settled down in the water during frying work so as to control oxidation of the oil and an increase of the water temperature, furthermore to avoid steam bubbles on the oil surface, which may bring difficulties in frying operation.
According to the conventional food fryer as described above, the temperature of the oil therein is usually heated up about 200 □ during the frying operation. And we must hence cool down the oil prior to cleaning the food fryer after the frying work. Furthermore, it is necessary to store the oil in a separate container and then to put it back to the food fryer, if the same oil is to be used repeatedly. In this way, it is not easy to handle the conventional food fryer.
In order to solve the problem of displacing the oil at this food fryer cleaning as described above, in U.S. Pat. No. 5,632,266 the inventor of this application disclosed a food fryer having an oil storage tank provided with each cock at its upper position and its lower position.
A preparation step in the above U.S. Patent for cleaning the oil layer area and the water layer area out the oil storage tank of the food fryer is explained hereafter as one example. It is optional whether water is to be put into the oil storage tank prior to frying anything or not: in this example the oil storage tank of the food fryer is filled with water by user's operation of closing the lower cock and simultaneously opening the upper cock, and closing the upper cock thereafter.
The preparation steps for cleaning are as follows.                (1) first, opening the lower cock of the oil storage tank to discharge water therein so as to being empty the tank and then closing the lower cock,        (2) second, opening the upper cock of the oil storage tank to fully move oil in the oil layer area to this tank, thereafter closing the upper cock,        (3) finally, opening a water discharge cock formed at the lowest end of the water layer area to drain water in the water layer area out.        
The food fryer after this preparation is put in steady state: the oil storage tank contains the oil, with both the upper cock and the lower cock closed; the oil layer area and the water layer area except the oil storage tank are in empty and these areas are in space coupled to outside of the food fryer through the water discharge cock; thereby capable of cleaning both the layers outside the oil storage tank.
After the layers are cleaned, the water discharge cock is to be closed and the upper cock of the oil storage tank is to be opened, where the oil in the oil storage would flow out by merely pouring water into the food fryer due to a difference in gravity between oil and water. This state is just ready for another food frying work.
The food fryer disclosed in U.S. Pat. No. 5,632,266 is good in use for improving the efficiency of the food frying operation.
And this food fryer has room for further improvement in product cost, assembling labor and handling performance of it because the oil storage tank comprises two cocks, the upper cock and the lower clock.
The object according to the invention is to reduce the cost and the labor for making the food fryer, and to improve frying and cleaning work by using an oil storage tank with an opening instead of the conventional upper cock, where an upper part of the opening is over its lower part and a lower cock of the oil storage tank is formed same as conventional.